The present invention relates to an exhaust apparatus for a combustion equipment, such as an internal combustion engine.
In previously proposed internal combustion engines, an exhaust apparatus includes an exhaust passage arranged within a water cooled cylinder head. With such exhaust apparatus, it is desirable to ameliorate an adiabatic performance thereof so as to minimize a decrease in temperature of exhaust gas. This results in, for example, an increase in initial conversion efficiency of a catalyzer for exhaust gas purification, an improvement in initial response characteristic of an oxygen sensor element, an increase in operating efficiency of a turbo charger, and the like. Thus, various kinds of exhaust apparatus including an exhaust liner have been proposed for this purpose.
Such exhaust apparatuses with improved adiabatic performance are classified into the following categories:
1. Exhaust apparatus which includes a layer of inorganic fiber as an exhaust liner which in turn includes a layer of ceramic thereinside (see JP-A 59-175693, JP-A 60-180659, and JP-U 60-149853),
2. Exhaust apparatus which includes a tubular member of ceramic as an exhaust liner, and has at least in part of the tubular member a reinforcement of zirconia and the like so as to surely hold the tubular member (see JP-A 60-169655),
3. Exhaust apparatus which includes a layer of flame sprayed ceramic as an exhaust liner (see JP-A 58-99180, and JP-U 62-40232).
A problem encountered in the aforementioned exhaust apparatuses in categories 1 and 2 is that the ceramic may be fractured by a thermal stress and/or a mechanical stress, and a temperature of exhaust gas may be reduced due to relatively large amount of heat conduction in a direction perpendicular to an exhaust gas flow.
Another problem encountered in the above-mentioned exhaust apparatus in category 3 is that the layer of flame sprayed ceramic may break away from the inner wall by a thermal stress and/or a mechanical stress.